Induction plasma generator with high velocity sheath



sept. 22, 1970 M. L. THORPE ET AL INDUCTION PLASMA GENERATOR WITH HIGH VELOCITY SHEATH Filed Feb. 5. 1969 4 Sheets-Sheet 1 Sept. 22, 1970 M, THORPE ETAL 3,530,335

` INDUCTION PLASMA GENERATOR WITH HIGH VELOCITY SHEATH Filed Feb. 5, 1969 4 Sheets-Sheet 2 E I l :F E@ OI :O z 4 :D 4 OI :Cl-'D IO OI |92 O2 I) CE IL |86 J 17e z Y W4 A i i .n w Y v i r l |76 f 3 [L wl i |70 I l r l |72 I L* I Sept. 22, 1970 M. L. THORPE ETAL 3,530,335

INDUCTION PLASMA GENERATOR WITH HIGH VELOCITY SHEATH Filed Feb. 5, 1969 64" |42.. 4 Sheets-Sheet 3 Vm 1" 11" d/62" j E: v

if; FIG 5 V I TV" V w I 66u l l. 202 7 l# eo" I 2z@ v 226 Sept. 22, 1970 M L THQRPE ETAL 3,530,335

INDUCTION PLASMA GENERATOR WITH HIGH VELOCITYv4 SHEATHA 4 Sheets-Sheet 4 Filed Feb. 5. 1969 FIG 8 GOIN FlG 9 w 2 w. w m ..2 n

'..O E... l w.. U... Il. ET. .LA|.2I\ BR Y .AF R C.T|Dr. E EN SO W LO BU OO lmA .8P R S UO A U OL G 4D! W T vm Y o W. 8 4 O 15m, sod 2595 United States Patent Oflice 3,530,335 Patented Sept. 22, 1970 U.S. Cl. 315-111 30 Claims ABSTRACT OF THE DISCLOSURE An induction plasma generator has a plasma forming chamber defined by a plurality of axially extending tubes surrounded by an electric field permeable, gas impermeable tube. An induction coil surrounds the tube. Extending into one end of this chamber is an assembly that defines a main gas injector and an auxiliary gas injector with a stabilizing structure separating the gas fiows from the two injectors.

The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

This application is a continuation-inpart of our copending patent application Ser. No. 667,786, filed Sept. 14, 1967, entitled Induction Plasma Generator.

SUMMARY OF INVENTION This invention relates to plasma generators and more particularly to apparatus for inductively heating a gas with high frequency electrical energy. Such generators create high temperature thermal plasma gas by inductively coupling high frequency electrical energy to ionized gas and are useful for a variety of purposes, including the production of chemical reactions, material testing and treatment, and general industrial heating.

An object of this invention is to provide novel and improved induction plasma generators.

Another object of this invention is to provide a novel and improved induction plasma generator configuration which provides stable operation with a variety of gases and a variety of operating conditions.

Another object of the invention is to provide novel and improved configurations of induction plasma generators particularly useful in industrial processes which involve either the heating of fluids or the injection of particles into a heated gaseous stream.

A more specific object of the invention is to provide a novel and improved system lfor transferring heat to a gaseous medium from a core of gas in plasma condition.

Still another object of the invention is to provide a system for simulating a gas core nuclear reactor, In one form such a reactor will employ a fssioning core of uranium surrounded by a sheath of hydrogen for ca'rrying away the heat and acting as a propulsion fluid for deep space exploration. An induction plasma generator constructed in accordance with the invention provides information on mixing and stabilization mechanisms that are likely to occur in such a gas core reactor propulsion unit; as Well as techniques for obtaining long retention times of the material in the heat generation core, and for increasing the efliciency of heat transfer to the gas sheath.

Another object of the invention is to provide novel and improved arrangements for the heating of gaseous stream and -materials carried by such streams.

A plasma generator constructed in accordance with a feature of the invention includes means defining a plasma chamber and an electrical coil surrounding the chamber for creating an electromagnetic iield within the chamber. A first gas input introduces a main gas for flow into the plasma chamber and conversion into plasma condition under the influence of the electromagnetic field produced by the electrical coil. A second gas input is provided for introducing gas in an annular sheath between the chamber wall and the plasma of the rst gas for transfer of heat from the plasma to the gas sheath. This gas sheath may be introduced into the plasma chamber in a variety of ways including transpiration through the wall of the plasma chamber or axial flow at high velocity along that wall. A stabilizing structure is interposed between the sheath gas and core gas adjacent the first turn of the coil so that a lower part of the plasma arc is within the structure and isolated from the sheath gas. This stabilizing structure may be located opposite the first turn of an axially disposed coil or on either :side thereof within an axial distance of one-half diameter of the core gas ow passage. The stabilizing structure preferably is permeable to the electric field and impermeable to the core and sheath gases.

In a particular embodiment, the second or auxiliary gas injector includes an axially extending annular passage of substantial length having an outer wall of the same configuration as the inner Wall of the plasma chamber and an inner wall that terminates at the beginning of the plasma chamber so that an outlet is defined between the inner and outer walls of the auxiliary gas injector structure supplies the sheath gas. The sheath gas is in- ,troduced at a position remote from that outlet for flow through the annular passage and entry into the plasma chamber in a symmetrical sheath having uniform axial flow characteristics. In this embodiment both the plasma and sheath gas injectors include means for discharging gas along a multiplicity of paths in directions that have radial components relative to the axis of the plasma generator against a wall portion so that those radial co-mponents of gas flow are converted into axial flow of uniform circumferential profile.

In one embodiment of the invention, the inner wall of the auxiliary injector structure includes a tubular member that has cooling fluid owing through it and a stabilizing structure in the form of a dielectric ring is mounted in it; while in another embodiment there is provided an intermediate buffer tube and a multiplicity of closely spaced, axially extending tubular elements disposed inside the buffer tube that extend to the beginning of the plasma region and provide a multiplicity of separate entrance and return paths for coolant fluid. In these embodiments the portions of the transition structures that are disposed in the main portion of the plasma maintaining electromagnetic ield are arranged to not signiiicantly absorb that eld, for example, a series of tubular elements arranged in a ring or a quartz barrier ring. Such structures may extend through the entire length of the plasma chamber.

An induction plasma system constructed in accordance with the invention has operated satisfactorily with a plate power in excess of eighty kilowatts, employing argon as the main (plasma forming) gas and hydrogen as the sheath gas, with hydrogen to argon velocity ratios in excess of 60 to 1, and in excess of 900 kilowatts with argon as the core gas and air as the sheath gas with sheath to core gas velocity ratios of 45 to l.

A further feature is the use of a one or more additional glas flow systems intermediate to the main and auxiliary gas flows to provide improved velocity matching and thus reduce mixing in the transition region between the main and auxiliary gas flows.

In accordance with another feature of the invention, the plasma chamber is defined by a multiplicity of axially extending spaced tubular elements disposed in a ring for defining a channel through which the plasma forming (core) gas flows. The tubular elements are arranged in groups. The ends of a rst portion of the tubes in each group are adapted to be connected to a source of coolant fluid adjacent the entrance end and the corre- Sponding ends of the remaining portion of the tubes in 'each group are adapted to be connected to a coolant sump also adjacent the entrance end. The other ends of the elements of each group are connected together at the exit end of the plasma chamber to provide a return path for coolant iluid. The plasma forming gas input is adjacent the connections at the entrance end and an electrical coil surrounds the chamber and is adapted to be connected to an oscillator for energizing the electrical coil to create an electromagnetic -eld within the chamber which converts the plasma forming gas into plasma condition. A tube of dielectric material is interposed between the ring of tubular elements and the electric coil. The coil may be located close to the exit end, thus permitting attainment of shorter overall length of the torch.

Apparatus constructed in accordance with one or more features of the invention increases the ease of operation of the torch (eg. the matching of the inductive load to the power supply). Further, the invention enables operation at higher power densities than heretofore obtainable with plasma generators of this type. The auxiliary (sheath) gas ow causes a reduction in the diameter of the plasma arc and provides additional protection for the wall of the plasma chamber. Velocity ratios up to 300:1 between the core gas and the auxiliary gas are made possible and the auxiliary gas has been used for such purposes as to transport particulate materials for heat treatment purposes or to provide an improved radiation barrier.

`Other objects, features and advantages of the invention will be seen as the following description of particular embodiments progresses, in conjunction With the drawings, in which:

FIG. 1 is a sectional View of a rst embodiment of an induction plasma generator constructed in accordance with the invention;

FIG. 2 is a sectional view, taken along the line 2-2 of FIG. l of the plasma chamber of the generator;

FIG. 3 is a sectional view of a second embodiment of a plasma generator constructed in accordance with the invention;

FIG. 4 is a sectional view along the line 4-4 of FIG. 3, details of the structure defining the wall of the plasma chamber;

FIG. 5 is a sectional View of still another embodiment of a plasma generator constructed in accordance with the invention;

FIG. 6 is a sectional view along the line 6-6 of FIG. 5;

FIG. 7 is a schematic diagram of electrical circuitry used with the induction plasma generator arrangements shown in FIGS. 1-6;

FIG. 8 is a sectional view of still another plasma generator embodiment; and

FIG. 9 is a graph indicating operating characteristics of the embodiment shown in FIG. 8.

DESCRIPTION OF PARTICULAR EMBODIMENTS The plasma generator as shown in FIG. 1 includes a base 10 having a central bore 12 in which a gas injector assembly 14 is mounted. A groove 16 in the bore houses an O ring 18 which is employed as a seal against the injector assembly and set screws 20 secure the injector assembly 14 in axial position relative to base 10.

The injector assembly includes a cylindrical body 22 (two inches in diameter) having a central material introducing passage 24 and three axially extending gas ow passages 26, 28, and 30. A counterbore 32 at the upper end of cylinder 22 provides a seat for a mixer head 40 which is secured in place by stud 42 (that has a hollow passageway 43 which is aligned with and forms an extension of passageway 24). Mixer head 40 includes a cylindrical block 44 (1.875 inch in diameter) having at its upper end an annular distributor channel 45 (0.062 inch deep and 0.312 inch wide) over which is secured a ring 46 having a series of twelve 0.026-inch axial discharge ports 47 disposed in it on 1.200 inch diameter center. Immediately below channel 45 are two peripheral distributor channels 48 (in communication with passage 26) and 50 (in communication with passage 30). On the wall of the seated mixer body is an annular ring 52 having a set of twelve radially extending ports 54 (each 0.026 inch in diameter) disposed immediately in front of distributor channel 48 and a set of twelve swirl ports 56' (each 0.026 inch in diameter) disposed in front of distributor channel 50.

Mounted on base 10 is a spacer 60 which houses a transition channel-auxiliary gas injector structure. Housing 62, in which induction coil 64 and plasma chamber defining quartz tube 66 are disposed, is in turn mounted on spacer 60. Through bolts 68 pass through base 10 and spacer cylinder 60 into housing 62 and secure that assembly together. End cap 70 on the upper end of housing 62 is secured in position by bolts 72.

Spacer cylinder 60 has an inner diameter of 31A inches and receives in sealing relation a stabilizing structure in the form of transition channel l and auxiliary injector structure 89. Transition channel structure 80, of two inches inner diameter and 4%; inches long, includes a water cooled section made up of walls 82 and 84, upper header 85, lower header y86 and cylindrical quartz separator 88 one-half inch in length, the end of which is locatedsubstantially in alignment with the lower power lead of coil 64. Surrounding transition channel 80 is an auxiliary gas injector structure 89 that includes an annular axially extending buffer passage 90, 1/16 inch in width, and a surrounding annular axially extending main passage 92, l3/16 inch in width. Auxiliary gas is supplied to buifer channel 90 through port 94 and passage 96; while the main ow of auxiliary gas is supplied through port 98 to distributor channel 100 and through radial ports 102 (42 in number, each 0.026 inch in diameter), and through a second main inlet including port 104 to distributor channel 106 and through swirl ports 108 (l2` in number, each 0.026 inch in diameter).

It will -be noted that the auxiliary gas distributor and transition channel structure, formed as an integral unit, are mechanically positioned with respect to injector structure 14 so that a precise coaxial configuration results. Quartz tube 88 forms an extension of the inner wall of transition structure 80 so that a smooth flow of plasma gas (separate from the auxiliary gas supplied by injector structure 89) is provided along the walls of the quartz extension 88.

A coolant passage inlet 110 extends from the mating surface between cylinder 60 and housing 62, to the channel between walls 82 and 84 and an outlet passage I112 extends radially outwardly from the channel between walls 82 and 84 at the side opposite inlet 110.

Housing 62, of a suitable material of uniform high dielectric integrity, which is unaffected by the coolant employed, a suitable material being polytetrafluoroethylene (Teflon), has attached tubular electrical terminals 120, 122, each of which has a water cooled passageway 124. The upper terminal is connected to terminal block 126, which in turn is connected to one end of coil '64 (5732 inch round copper wire wound to provide ve turns over a length of about 4 inches, about 31A inch I.D.). The other end of coil 64 is connected to block 128 to which terminal 122 is threadedly connected. The coolant passage 124 of terminal 122 is connected to passage 130 in housing 62 which passage is in turn aligned with passage 110- in section 60. A second passage 132, connected to annular chamber 134 in which coil 64 is disposed, permits coolant ow upwardly past coil 64 and around the upper end of quartz tube 66 for return through exit passage 136 to the passage 124 in upper terminal 120.

The nozzle 140 secured to end cap 70 provides a restricted orifice through which both the plasma gas and the auxiliary gas flows. In addition, the nozzle structure extends down into the plasma chamber delined by quartz tube 66 sufficiently to interpose a shield opaque to radiation from the arc region between that arc region (indicated at 142) and the upper quartz tube support O ring 144. The transition channel structure 80 provides a similar radiation opaque protective shield for lower O ring 146. A number of other O ring seals 148 are provided between the mating components of the generator, end cap 70 and housing 66; housing 66 and cylinder 60; and auxiliary injector 89 and cylinder 60 and base 10.

In a typical operation of this plasma generator a plasma is initiated by introducing argon gas at 30 s.c.f.h. through axial inlet ports 46 (passage 28) and 80 s.c.f.h. through inlet ports 56 (passage 30). The plasma may be initiated by suitable means such as temporary insertion of a graphite rod into the plasma chamber where it is heated by the electromagnetic eld established by coil 64. After the plasma is created, the plasma sustaining argon flow is adjusted to the following values:

Passage: S.c.f.h. 26 40 The resulting arc 142 is of configuration generally as indicated in FIG. 1. A gas for chemical reaction or for analysis purposes may be supplied through ports 94, 98, and A104. Port 94 is primarily for buffering purposes while the main gas ow is through port 98 (added gas through port 104 is generally not desirable). With this apparatus hydrogen as the auxiliary gas has been heated to a temperature of 2800 F. at a flow rate of 3600 s.c.f.h. distributed among the auxiliary ports in the following quantities:

Port: S.c.f.h. 94 20D-1000 98 Z600-3600 in a continuous operation over one hour without creating unstability in the arc 142. At lower flow rates hydrogen introduced through the auxiliary injector 89 has been heated up to 50G-0 F.

A second embodiment is shown in FIGS. 3 and 4. That plasma generator has a base in which is supported a plasma gas (main) injector structure diagrammatically indicated at 40 and an auxiliary gas injector transition channel structure 60. Disposed in structure 60 is a transition channel insert 150, 2.1/8 inches in inner diameter, and 61/2 inches in length. This transition channel 150 includes a base 152 which is threadedly secured to the section 60'; an inner metal wall 154 to which is secured a header 156 on which is received quartz tubular extension 158; and a surrounding tubular wall member 160 which depends from header 156 and forms with wall 154 an annular coolant channel `162.

A third tubular member 164, also secured to header 156, has a series of 42 axial ports 166 (0.026 inch in diameter) and a series of 6 swirl ports 167 (0.026 inch in diameter) in communication With annular chamber 168 formed between members 160 and 164. This insert structure 150 is secured in structure 60 which includes coolant inlet 170, coolant outlet 172, and auxiliary gas inlet 174. O ring 176 provide seals to isolate the coolant from the auxiliary gas.

Mounted on spacer 60' is a plasma chamber defining structure which includes a base 180 (functioning as a header) to which are secured in a ring a series of 1/s inch O.D., 0.085 I.D. copper tubes spaced 0.022 inch apart. The lower ends of the tubes are soldered to base 180 for communication with distributor channel y184 which in turn is connected to inlet port 186 and outlet port 188. The upper ends of tubes 182 are similarly connected to header 190. The distance between headers 180 and 190 is 5% inches and the inner diameter of each header is three inches.

Surrounding the set of tubes 182 is a ceramic (Rotasil) tube 192, 31/2 inches I.D. and 71A inches long. A SiX turn induction coil 64 of 1A inch O.D. copper tubing surrounds the tube 192 and is connected to the power supply.

The use of this metal wall structure to dene the plasma chamber has been found to have particular advantage in operating the generator without auxiliary gas flow. For example, generators in which the plasma chamber is defined by the ring of metal tubes have been operated with percentages of hydrogen in the main gas ow in excess of those percentages which would cause cracking of the quartz tube in a generator of the type shown in FIGS. l and 2. Further, higher power densities were employable with the ring of tubular elements. In such a generator employing a one inch diameter plasma chamber formed of tubular elements, the system Was operable when a power of kilowatts in the arc while 17 kilowatts was the maximum operating power in the arc using a one inch diameter quartz tube when operating with air as the plasma gas.

Ignition of this plasma generator conguration may be obtained by contacting a graphite stud 43 of mixer 40 with an energized electrode introduced axially through the discharge end of the plasma chamber. A DC arc is drawn, ionizing gas in the chamber to which the electric eld produced by coil 64 couples.

Operation of the plasma generator shown in FIGS. 3 and 4 with the following values has been obtained:

Argon center cores.c.f.h.

Hydrogen sheath-2730 s.c.f.h.

Coil turns-6 Coil I.D. 4 inches Oscillator tank capacitor-900 microfarads Blocking capacitor-125 microfarads Frequency- 2.5 mc.

In a modification of the plasma generator structure shown in FIG. 3, the plasma chamber structure shown in FIG. 1 may be substituted while locating the coil 64 at the end of the quartz extension 158 in the same relation as shown in FIG. 3. Operation with the following values (which may be compared with those indicated above) was obtained:

Argon center cores.c.f.h.

Hydrogen sheath-3610 s.c.f.h.

Coil turns-S Coil I.D.-3.3 inches Oscillator tank capacitor-900 microfarads Blocking capacitor-200 microfarads Frequency-3-l Inc.

The heat energy in the gas leaving the torch was measured to be in excess of 40% of the DC input energy to the generator.

Still another embodiment is shown in FIGS. 5 and 6. That plasma generator has a base 10 in which is supported a plasma gas (main) injector structure diagrammatically indicated at 40 and an auxiliary gas injector structure 60". Secured to structure `60 and extending upwardly therefrom is a transition channel structure in the form of fiftyeight tubes 200 of one-eighth inch outer diameter and 0.085 inch inner diameter. The tubes are spaced approximately 0.020 inch apart (although satisfactory operation is obtained with several (but not all) tubes of adjacent pairs in contact with one another) and a suitable gas barrier such as Sauereisen cement is disposed in the spaces between the tubes 200. The upper ends of each pair of tubes 200 are soldered together to provide a return How passage. Outside the ring of tubes 200 is a buffer tube of quartz 202 and surrounding tube 202 is the plasma chamber tube 66 which is surrounded by coil 64".

The auxiliary injector structure 60 includes a cooling water entrance port 210 connected through a passage 212 to manifold 21`4 which communicates with every other tube 200; and a cooling water discharge port 216 connected through passage 218 to a similar manifold v 220 which is connected to the other tube of each pair for providing a return path for the flow of cooling water. Buffer gas is supplied through port 222 to a series of axial ports 224 for impingement against the outer wall of the ring of tubes 200 and conversion to axial ow between that ring of tubes and quartz tube 202. The port 226 through which the sheath gas is introduced is in communication with a manifold ring 228 and a series of radial ports 230 which discharge the sheath gas against the outer wall of buffer tube 202 where the ow is converted into axial direction flow between tubes 202 and 66 upwardly into the plasma chamber.

A three-turn induction coil 64 of double solid copper Wire surrounds tube 66" and is connected to the power supply.

Stable operation of the plasma generator shown in FIGS. and 6 with the following values has been obtained:

S.c.f.h. Argon core 120 Hydrogen buffer 500-800 Hydrogen sheath 3000 The flow of sheath gas may be varied over the range of 0-5000 s.c.f.h. with a constant core gas flow of 120 s.c.f.h. without instability in the operation of the system. The arc 142 in the vicinity of the rst (lowest) turn of the coil 64 is the most radiant and it is preferred to locate the upper end of the transition structure relative to coil 64 so that the arc 142 is within the stabilizing separator structure as shown in FIG. 5. However, satisfactory operation of the system is obtained with the end of the separator flush with the end of coil 64", one-half inch into that coil or one-half inch spaced from that coil.

A schematic diagram of an electrical system used with these plasma generators is shown in FIG. 7. That system includes an oscillator tube 240 to which DC power is applied over lines 242, 244. The input power is measured by ammeter 246 and voltmeter 248. Capacitor 250 and inductor 252 provide a lter network. A tuning circuit for the grid (control electrode) 254 includes ca- Percent plate kw. Argon core, Sheath, Plate, leaving s.c.f.h./dia., type/ Buffer gas, Torch dia. kw. torch inches s.e.f.h. type/seth.

87. 5 45. 7 120/2 H2/3,100 Ilz/1,000 84. 2 43. 0 102/2 Iig/3,100.. 11g/850 72. 2 39. 2 120/2 B27/2,80 0 620 8 740/3. 5 Air/2,200 0 870 2 740/3. 5 Air/2,200. 0 770 36. 2 48/3. 5 Air/2,340 0 150 18. 6 787/5 Ai1/750. 0 203 20. 0 787/5 Ai1`/2,200 0 425 33. 4 787/5 Air/2,200 0 721 38. 5 413/5 Air/2,200 0 967 33. 0 787/5 Air/2,20() 0 A further embodiment is shown in FIG. 8. That plasma generator has a base 10', in which is supported a plasma gas injector structure of the same general type as shown in FIG. l and diagrammatically indicated at 40". Secured to injector structure 40 is a plasma chamber defining structure (about 1.1 inch in diameter) in the form of twenty-eight tubes 280 of one-eighth inch outer diameter and 0.085 inch inner diameter. The tubes are spaced approximately 0.020 inch apart. The upper ends of each pair of tubes 280 are soldered together to provide a return coolant flow passage in the same manner as the tubular structure shown in FIGS. 5 and 6. Sauereisen cement is disposed in the spaces between the tubes 280'. Outside vthe ring of tubes 230 is a 1.5-inch LD., 6-inch long dielectric tube 282 of quartz and surrounding and spaced 0.125 inch from tube 282 is a water cooled electrical coil 64".

Torch operation with pure hydrogen was achieved with a coil 64 of seven turns and a tank circuit that had a capacitance of 1200 picofarads and a total circuit inductance, including coil 64"', of approximately 1 microhenry. The torch was operated vertically and in open air. The unit is ignited on pure argon at a flow rate of 100 s.c.f.h. and the power increased to 100 kilowatts. Hydrogen at a flow rate of six s.c.f.h. was then added to the argon ignition ow rate and then the argon was turned off.

Operating limits of this torch are indicated in FIG. 9, The upper limits of stable operation are a function of the particular power supply and coil configuration employed. Typical operating conditions for air, hydrogen, helium and argon are indicated in the following table:

Hydrogen Typical Operating point air A B G Helium Argon KW. plate power 95.0 110. l 114. l 103. 7 57 80 Work coil turns 8 7 7 7 7 4 Torch I D., inches 1. 1 1. 1 1. 1 1. 1 l. 1 1. 1 Gas flow, s e fh 115 10.0 6. 0 4. 5 60 340 Percent plate power to exit gas 30.0 13.8 12.8 14. 38 7. 38 50. l Average exit gas enthalpy, B.t.u./lb 11, 100 591, 000 l, 504, 000 2, 162, 000 23, 200 3, 800

Letters refer to operating point on Fig. 9.

pacitors 256, 258, inductors 260, 262 and resistor 264. Ammeter 266 is provided for measuring current flow to the grid circuit. The plate (output electrode) 268 of tube 240 is coupled by blocking capacitor 270 to the main tank circuit that includes tank capacitor 272, generator coil 64 and adjustable inductor coil 274.

With this system a plasma condition is initially established. The auxiliary gas stream (gas to Which heat is to be transferred) is then introduced in the annular sheath surrounding the established plasma arc. The use of one or more buffer gas flows moderates the velocity transitions between the plasma core gas and the sheath gas where that sheath has a high velocity and tends to produce a larger diameter arc of increased stability.

The high exit gas enthalpies produced with this torch (radiative components of the exit gas enthalpies being measured with a High Cal Engineering detector #C- 7015 are of note. This tubular structure produces a lower reflected resistance under equivalent arc conditions and permits the electrical coil 64 to be located closer to the exit from the plasma chamber, resulting in a shorter torch and more power in the exit gas as less heat is lost to the torch walls. The arc projects substantially beyond the end of the plasma chamber and such device is useful as a highly radiative light source.

Apparatus constructed in accordance with the invention permits effective gas core reactor simulation with hydrogen sheath to argon core velocity ratios greater than 30 to 1. Efficient heat transfer to the auxiliary gas is produced with stable operation permitting higher power operation. The systems produce intense radiation and thus are useful as light sources, in addition to material treatment.

While particular embodiments of the invention have been shown and described, various modifications thereof will be obvious to those skilled in the art. For example, the specific dimensions and configurations of the described embodiments are for the purposes of illustration and are not intended as limitations other than as stated in the claims. It is therefore not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. An induction plasma generator comprising means defining a plasma chamber,

a first gas input for introducing a first gas for flow into said plasma chamber,

ane electric coil surrounding said chamber for creating an electromagnetic field within said chamber to convert said first gas to a stable plasma arc condition, said first gas input providing sufficient gas to establish and maintain said stable arc condition without gas from any other source,

an auxiliary gas input for introducing further gas for fiow at a higher fiow rate than the fiow rate of said first gas in an annular sheath between said stable plasma arc condition and the wall of said chamber for transferring heat to said further gas from said stable plasma arc condition,

and a stabilizing structure disposed adjacent the first turn of said coil so that the lower part of said stable plasma arc condition is within said stabilizing structure and isolated from said sheath gas by said stabilizing structure so that said stable arc condition is maintained notwithstanding the flow of said further gas at a ow rate sufiicient to cause extinguishment of said stable plasma arc condition in the absence of said stabilizing structure.

2. The plasma generator as claimed in claim 1 wherein said auxiliary gas input includes a passage of substantial length, the outer wall of said passage being of the same configuration as the inner wall of said plasma chamber, the inner wall of said passage terminating near the end of said electrical coil so that an outlet is defined between said inner and outer walls of said auxiliary gas input, and means at a position remote from said outlet for introducing gas into said annular passage for axial ow therethrough and into said chamber in a uniform symmetrical sheath.

3. The plasma generator as claimed in claim 2 further including structure disposed between said auxiliary gas input and said first gas input including a multiplicity of axially extending, spaced tubular elements disposed in a ring, and means to flow coolant fluid to said tubular elements.

4. The plasma generator as claimed in claim 3 wherein said tubular elements are arranged in pairs, the elements of each pair being connected together at one of their ends, the other end of one tube of each pair being adapted to be connected to a source of coolant fluid and the other end of the other tube of each pair being adapted to be connected to a coolant sump.

S. The plasma generator as claimed in claim 1 and fur ther including a buffer gas input for supplying another gas flow in an annular stream between said auxiliary sheath gas and said plasma gas at a velocity intermediate the velocities of said plasma gas and said sheath gas.

6. The plasma generator as claimed in claim 5 wherein said buffer gas input includes a gas impermeable axially extending annular wall structure between said first and auxiliary gas inputs for separating the flows of said plasma, buffer and auxiliary gases from one another.

7. The plasma generator as claimed in claim 1 wherein said auxiliary gas input includes an auxiliary extending annular passage having an outlet adjacent the first turn of said electrical coil, the structure defining said outlet being permeable to the electromagnetic field created by said electric coil and impermeable to the plasma and auxiliary gases.

8. The plasma generator as claimed in claim 1 wherein said stabilizing structure is permeable to the electric field created by said electric coil and impermeable to said core and sheath gases.

9. The plasma generator as claimed in claim 8 wherein said stabilizer structure includes a plurality of spaced tubular elements arranged in a ring..

10. The plasma generator as claimed in claim 8 wherein said stabilizing structure includes a cylinder of dielectric material.

11. The plasma generator as claimed in claim 1 wherein said auxiliary gas input includes means for introducing gas for fiow in said annular sheath as a velocity substantially greater than the velocity of the plasma gas introduced through said first gas input.

12. The plasma generator as claimed in claim 1 wherein each said gas input includes means for discharging gas along a multiplicity of paths in a direction that has a radial component relative to the axis of the plasma generator, and a wall portion disposed opposite each said gas discharging means for converting the gas flow along said multiplicity of paths to fiow in the axial direction into the plasma chamber.

13. The plasma generator as claimed in claim 1 and further including a high frequency oscillator for energizing said electrical coil, said oscillator including a control device having an output circuit and a control electrode, and a tank circuit connected across the output circuit of said control device, said tank circuit including said electrical coil and a capacitor.

14. The plasma generator as claimed in claim 13 wherein said auxiliary gas input includes an axially extending passage of substantial axial length the outer wall of said passage being of the same configuration at the inner wall of said plasma chamber, the inner wall of said passage terminating at the end of said electrical coil so that an outlet is defined between said inner and outer walls of said auxiliary gas input, and means at position remote from said outlet for introducing gas into said annular passage for axial flow therethrough and into said chamber in a uniform symmetrical sheath.

15. The plasma generator as claimed in claim 14 wherein said axially extending passage includes an outlet defining structure, said outlet defining structure being permeable to the electromagnetic field created by said electric coil and impermeable to the plasma and auxiliary gases.

16. The plasma generator as claimed in claim 15 further including structure disposed between said auxiliary gas input and said first gas input including a multiplicity of axially extending, spaced tubular elements disposed in a ring, and means to flow coolant fluid to said tubular elements.

17. The plasma generator as claimed in claim 16 wherein said tubular elements are arranged in pairs, the elements of each pair being connected together at one of their ends, the other end of one tube of each pair being adapted to be connected to a source of coolant fluid and the other end of the other tube of each pair being adapted to be connected to a coolant sump.

18. The plasma generator as claimed in claim 17 and further including a buffer gas input for supplying another gas iiow in an annular stream between said auxiliary sheath gas and said plasma gas at a velocity intermediate the velocities of said plasma gas and said sheath gas, said buffer gas input including a gas impermeable axially extending annular wall structure between said first and auxiliary gas inputs for separating the liows of said plasma, buffer and auxiliary gases from one another.

19. The plasma generator as claimed in claim 17 wherein said plasma and auxiliary gases are different gases and said auxiliary gas input includes means for introducing gas for -flow in said annular sheath at a velocity substantially greater than the velocity of the plasma gas introduced through said first gas input.

20. The plasma generator as claimed in claim 19 wherein each said gas input includes means for discharging gas along a multiplicity of paths in a direction that has a radial component relative to the axis of the plasma generator, and a wall portion disposed opposite each said gas discharging means for converting the gas fiow along said multiplicity of paths to flow in the axial direction into the plasma chamber.

2.1. An induction plasma generator comprising means defining a plasma chamber,

an electrical coil surrounding said chamber and adapted to be connected to a source of electrical energy for creating an electromagnetic field within said chamber,

a gas input at one end of said plasma chamber -for introducing a gas for flow into said plasma chamber and conversion into plasma condition under the influence of said electromagnetic field, a multiplicity of axially extending spaced tubular elements disposed in a ring for defining a channel through which said first gas ows, said tubular elements being arranged in groups, with one end of each tube in a first portion of the group being adapted to be connected to a source of coolant fluid and the corresponding end of each tube in the remaining portion of the group being adapted to be connected to a coolant sump and the other ends being connected together to provide a coolant flow path between said first portion of tubes and the remaining portion of tubes in each group, and means for preventing ionized gas from migrating from said plasma chamber to said electrical coil.

22. The plasma generator as claimed in claim 21 and further including an auxiliary gas input for introducing a gas in an annular stream outside of and surrounding said first gas for flow through said plasma chamber past the plasma arc of said first gas, said auxiliary gas input being adapted to introduce gas for flow in said annular sheath at a velocity substantially greater than the velocity of the plasma gas introduced through said first gas input, and including an axially extending passage of substantial axial length, the outer wall of said passage being the same configuration as the inner wall of said plasma chamber, the inner wall of said passage terminating Vat the end of said electrical coil adjacent said gas input so that an outlet is defined between said inner and outer Walls of said auxiliary injector, and means at a position remote from said outlet for introducing gas into said annular passage for axial ow therethrough and into said chamber in a uniform symmetrical sheath.

23. The plasma generator as claimed in claim 22 wherein each said gas input includes means for discharging gas along a multiplicity of paths in a direction that has a radial component relative to the axis of the plasma generator, and a wall portion disposed opposite each said gas discharging means for converting the gas flow along said multiplicity of paths to flow in the axial direction into the plasma chamber.

24. The plasma generator as claimed in claim 22 and further including a buffer gas input for supplying another gas fiow in an annular stream between said auxiliary sheath gas and said plasma gas at a velocity intermediate the velocities of said plasma gas and said sheath gas, said buffer gas input including a gas impermeable axially extending annular wall structure between said first and auxiliary gas inputs for separating the flows of Said plasma, buffer and auxiliary gases from one another.

25. The plasma generator as claimed in claim 22 wherein said auxiliary gas input includes an axially extending annular passage having an outlet adjacent the first turn of said electrical coil, the structure defining said outlet being permeable to the electromagnetic field created by said electric coil and impermeable to the plasma and auxiliary gases.

26. The plasma generator as claimed in claim 21 wherein said plasma chamber defining means includes said ring of tubular elements said gas migration prevention means includes a tube of dielectric material interposed between said ring of tubular elements and said electrical coil.

27. An induction plasma generator comprising means defining a plasma chamber,

a high frequency electrical coil surrounding said chamber for creating an electric field within said chamber,

a main gas injector spaced from one end of said chamber for introducing a first gas for flow into said plasma chamber and conversion to plasma arc condition under the influence of said electric field,

a stabilizing structure of smaller cross-sectional dimension than said plasma chamber for introducing said first gas from said main injector to said plasma chamber in the vicinity of said electrical coil in a main stream coaxial with and spaced from the wall of said plasma chamber, and

an auxiliary gas injector for intrducing a second gas in an annular stream outside of and surrounding the stream of said first gas for fiow through said plasma forming chamber past the plasma arc of said first gas, said auxiliary gas injector including an axially extending annular passage of substantial length, the outer wall of said passage being of the same configuration as the inner wall of said plasma chamber, the inner wall of said passage terminating at said stabilizing structure so that an outlet is defined between the inner and outer walls of said auxiliary injector adjacent said stabilizing structure, and means at a position remote from said outlet for introducing said second gas into said annular passage for fiow past said stabilizing structure in a uniformly symmetrical sheath.

28. The plasma generator as claimed in claim 27 wherein said main gas injector includes means for introducing said first gas for ow in an axial direction into said plasma chamber, and independently controllable means for imparting a tangential component for stabilization purposes to the oW of said first gas.

29. The plasma generator as claimed in claim 28 Wherein each said injector includes a means for discharging gas along a multiplicity of paths in a direction that has a radial component relative to the axis of said plasma generator and a wall portion disposed opposite each said gas discharging means for converting said gas moving in said multiplicity of paths to flow in the axial direction. f 30. The plasma generator as claimed in claim 27 wherein said stabilizing structure is a tubular structure that eX- tends from said main injector to said plasma chamber and surrounds a portion of the arc produced under the influence of said electric eld. I

References Cited UNITED STATES PATENTS 3,246,115 4/1966 Johnson 219-121 3,264,508 8/1966 Lai et al. 315--111 X 3,301,995 1/1967 Eschenbach et al 219-121 3,324,334 6/1967 Reed 313-231 3,347,698 10/1967 Ingham 219--121 X 3,373,306 3/1968 Karlovitz 313-231 JAMES w. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner Us. o1. X.R. S13-231 

